1. Field of the Invention
The present invention is directed to novel polyphenylene ether-polyethylene copolymer blends prepared by reactive melt blending of polyphenylene ether or an ester end-capped polyphenylene ether with an ethylene-acrylic acid copolymer.
2. Discussion of the Background
The polyphenylene ether resins (PPE) constitute a family of high performance engineering thermoplastics possessing outstanding properties, such as relatively high melt viscosities and softening points, which make them useful for many commercial applications. More precisely, PPE resins are suitable for many commercial applications requiring high temperature resistance and including formation of films and molded articles.
Among the most important characteristics of PPE resins are excellent hydrolyric stability, dimensional stability, toughness, heat resistance and dielectric properties.
On the other hand, PPE resins, although displaying the above-mentioned desirable properties, are also endowed with certain unsatisfactory properties which render them undesirable for many commercial uses. For example, films and fibers can be formed from polyphenylene ether resins on a commercial scale using solution techniques but melt processing is commercially limited because of the high temperatures required to soften the PPE resins which cause instability and changes in the polymer structure. Further, PPE polymers tend to degrade and to grow dark during melt processing.
Moreover, PPE resins are brittle due to their poor impact strength and limited in tensile properties and they are endowed with poor solvent resistance as well, and therefore cannot be used in applications, such as automotive applications where the parts will be exposed to chemicals, such as gasoline, grease and detergents. Therefore, there is a continuing search for improving the deficient characteristics of PPE particularly workability and solvent resistance.
In order to improve molding properties and impact strength, polyblends of polyphenylene ether resins with styrene resins have been employed. Thus U.S. Pat. No. 3,363,435 discloses that PPE can be mixed with polystyrene (PS) in all proportions to give blends with a good combination of properties and enhanced molding properties. However, the range of application of PPE-PS blends is still limited due to poor solvent resistance, i.e., they are unsuitable in fields requiring resistance to oils and gasoline.
In order to overcome the poor solvent resistance of PPE a number of blend compositions of polyolefins and PPE have been proposed. For instance U.S. Pat. No. 3,361,851 reported blends of PPE with small quantities (up to ten percent) of polyethylene (PE) which result in some improvements in both the impact strength and solvent resistance of PPE.
Other PPE-PE blends displaying a better set of properties with reference to PPE resins alone have been disclosed in U.S. Pat. No. 4,166,055, Japanese Patent Publication No. 7069/67, Japanese Patent Application Nos. 71,158/78 and 88,960/79.
It has been shown that polyolefins, particularly polyethylene (PE), even when added in small amounts, can noticeably change some characteristics of the PPE and therefore constitute an excellent component at very low price in the binary blends with PPE and in ternary blends with PPE and PS resins. Preferred amounts of PE in such blends range from 1 to 10% by weight (U.S. Pat. No. 3,361,851; U.S. Pat. No. 4,584,334), and are sufficient to improve their impact and cracking resistance.
Moreover PE acts as a plasticizer for PPE and the resulting blends are endowed with enhanced workability and better surface appearance (U.S. Pat. No. 3,809,729; DE 57,139,140; U.S. Pat. No. 4,145,377; U.S. Pat. No. 4,584,334).
Among other properties which are improved by adding small amounts of PE, the most important is the oxidation resistance of the melted PPE blends. PPE resins containing small amounts of polyethylene do not grow dark during melt processing.
Nevertheless, PPE-PE blends fail to take full advantage of organic solvent resistance inherent in polyolefins because either the amount of the polyolefin is too small or PPE and PE resins are not very compatible at higher compounding ratios exceeding 3-5% by weight of PE. The same incompatibility has been observed in PPE blends with high molecular weight polyolefins. In compositions composed of polyphenylene ether and either high molecular weight polyolefin or polyolefin exceeding 3-5% by weight, the two polymers are not uniformly mixed with each other and form a "sea-island" structure according to U.S. Pat. No. 4,460,743. Consequently, the resulting composition is fragile and has reduced mechanical strength and impact strength. When injection molded, the two polymers tend to agglomerate in the direction of the resin stream due to their essentially poor compatibility with each other and the resulting moldings are delaminated in a laminar state, thus being unsuitable for practical use. The use of lower molecular weight polyolefins do not solve the problem of the incompatibility either.
One way to overcome these drawbacks and increase the amount of compatible PE in PPE-PE blends is to add styrene (co)polymers or block copolymers of styrene and a conjugated diene as compatibilizers of the same blends. In the Japanese Patent Application No. 76547/85 it has been asserted that using a styrene-butadiene block-copolymer as a compatibilizer, the compatibility between PPE and PE resins can be improved up to 20% by weight of PE. Similar results have been disclosed in Japanese Patent Applications Nos. 71158/78, 88960/79 and 100159/84.
Although these compositions show improvements in molding properties, they fail to take advantage of the organic solvent resistance inherent to polyolefins from the point of view that the compounding ratio of the polyolefin in the composition is still too small or that the continuous phase is PPE or PPE-PS. Moreover, blends of PPE with block-copolymers of styrene have limitations to their use due to their inferior stiffness and tend to exhibit delamination (U.S. Pat. No. 4,322,507).
A second and probably preferred method of compatibilization of PPE with PE, is the use of PPE-PE copolymers. When present in the blend, these copolymers serve as compatibilizers for the uncopolymerized constituents, namely PPE and PE (U.S. Pat. No. 5,010,144; U.S. Pat. No. 4,460,743). Moreover, it has been shown that PPE-PE (grafted) copolymers can be compounded with styrene resins and give rise to perfectly compatible compositions (U.S. Pat. No. 4,460,743).
Several ways to obtain copolymers (or grafted copolyymers) of PPE with PE have been so far proposed. In U.S. Pat. No. 4,460,743 a polyphenylene ether-grafted polyolefin has been disclosed which has been obtained by reacting a glycidylated PPE with a polyolefin having anhydride groups or conversely by reacting a polyphenylene ether having anhydride groups with a glycidylated polyolefin. In U.S. Patent Application No. 07/351,905 PPE-PE copolymers have been obtained by reaction of a functionalized olefin polymer with a PPE which has been previously capped with an epoxychlorotriazine. A similar method giving the same copolymers is described in U.S. 5,010,144.
An even more complicated way to obtain PPE-PE copolymers or grafted copolymers has been disclosed in U.S. 4,914,153. According to this patent PPE-PE graft copolymers are obtained "in situ" by melt-kneading a modified (with maleic anhydride) polyphenylene ether with modified (with maleic anhydride) polyolefin and in the presence of a binder such as phenylenediamine.
It is apparent that all the proposed methods of compatibilizing PPE with PE resins are more or less complicated and expensive.
Therefore the problem of obtaining stable and compatible PPE compositions endowed with better processability and impact properties together with outstanding solvent resistance still exists.
Furthermore, the problem still exists of obtaining PPE resins containing PE polymers in such amounts as to display superior properties without any loss of compatibility between the components and still more without the need of adding considerable amount of compatibilizers such as styrene (co)polymers or block-polymers.